The invention relates to a monitoring installation such as is typically used for monitoring rooms accessible to the public, such as shops and large stores containing goods for sale. As a rule these monitoring installations should fulfill two aims, to wit: supervise the shop and the goods exposed therein, which is usually done optically, and also act as a deterrent for would-be thieves. Both aims require the use of a comparatively large number of monitoring units per square meter of surface to be surveyed, where each monitoring unit contains the necessary cameras, video-recorders etc. However, both for keeping the expenses down and in order to simplify the monitoring process one endeavours to use as few monitoring units as possible, even in large rooms. For a good exploitation of the units one sometimes uses stationary units which either contain several cameras or are constructed in such a way that they can rotate around a vertical and a horizontal axis. But even then the range covered by a single monitoring unit remains rather restricted, and thus necessitates using numerous monitoring unit in order to survey a large surface.
Hence it is a general object of the invention to fulfill both above-mentioned aims with the least possible number of monitoring units. To achieve this, the invention is defined as recited in claim 1. Accordingly, the invention allows one to monitor a very large surface even when the presence of high shelves makes it impossible to survey a large domain from far away or with the help of wide-angle and/or zoom-lenses. Further, the invention makes it possible to obtain with one or only a few monitoring units a deterrent effect that even exceeds that of a large number of usual stationary monitoring units. Indeed, the seemingly purposeful movement of a single unit above the head of a would-be thief, or along a path which he follows among the exposed goods, has a more disturbing effect than the quiet presence of stationary monitoring units with a view angle which the would-be thief can evaluate, or believes he can evaluate.